模拟失重条件下大鼠比目鱼肌肌梭神经营养因子3表达降低

Decreased neurotrophin-3 expression of intrafusal muscle fibers in rat soleus muscles under simulated weightlessness

本研究旨在探讨模拟失重对大鼠比目鱼肌肌梭神经营养因子3(neurotrophin-3,NT-3)表达的影响。采用大鼠尾部悬吊法建立模拟失重动物模型,按体重配对原则随机将大鼠分为5组,即尾悬吊3d组、7d组、14d组、21d组和正常同步对照组。采用免疫组织化学ABC染色法及酶联免疫吸附实验法(ELISA)检测大鼠比目鱼肌肌梭NT-3的表达。结果显示,大鼠比目鱼肌梭外肌中未见到NT-3表达;正常对照组大鼠比目鱼肌肌梭中,核袋1和核袋2纤维NT-3呈现强阳性表达;模拟失重后,梭内肌纤维的NT-3免疫染色反应进行性降低;NT-3的ELISA定量检测结果显示,正常组、尾悬吊3d组、7d组、14d组和21d组大鼠比目鱼肌NT-3的含量分别为(14.23±1.65)、(14.11±1.53)、(13.09±1.47)、(12.45±1.51)和(9.85±1.52)pg/mg。统计比较显示,尾悬吊14d后,大鼠比目鱼肌NT-3的含量较正常对照组明显减少(P<0.05);而尾悬吊21d后,大鼠比目鱼肌NT-3的表达进一步减少(P<0.01)。以上结果表明,模拟失重可致大鼠比目鱼肌肌梭NT-3的表达明显减少,并且随着模拟失重时间的延长,梭内肌NT-3的表达量进行性减少。提示微重力环境下本体感觉的适应性变化可能与肌梭NT-3的表达减少有关。

The present study aimed to study the changes of neurotrophin-3 （NT-3） expression of intrafusal muscle fibers in rat soleus muscles under simulated weightlessness. The tail-suspension （SUS） rat model was used to simulate weightlessness. Forty mature female Sprague-Dawley rats were randomly assigned to ambulatory control （CON）, 3-day SUS, 7-day SUS, 14-day SUS and 21-day SUS groups. Immunohistochemistry ABC staining method and enzyme linked immunosorbent assay （ELISA） were used to detect the NT-3 expression of intrafusal muscle fibers in rat soleus muscles. The results from the immunohistochemistry staining technique showed that the extrafusal muscle fibers did not exhibit the NT-3-like immunoreactivity, and NT-3-like immunoreactivity was mainly expressed in nuclear bag 1 and nuclear bag 2 fibers of the muscle spindles. The ELISA results showed that the expression quantity of NT-3 in rat soleus muscles in control, 3-day SUS, 7-day SUS, 14-day SUS and 21-day SUS groups were （14.23±1.65）, （14.11±1.53）, （13.09±1.47）, （12.45±1.51） and （9.85±1.52） pg/mg of tissue respectively. Compared to the control group, the expression quantity of NT-3 was significantly decreased after 14 days of SUS （P〈0.05）. After 21 days of SUS, the NT-3 expression was further reduced （P〈0.01）. These results suggest that simulated weightlessness induces an obvious decrease in the NT-3 expression level of intrafusal fibers in rat soleus muscles. Accompanying the simulated weightlessness extension, NT-3 expression in rat soleus muscle spindles is progressively decreased. These changes may contribute to the proprioceptive adaptations to microgravity.